A) An in vitro replication system for bacteriophage N4 has been developed to study the mechanism of its DNA replication. The system mimics in vivo DNA replication. The DNA replication proceeds continuously from both ends of the DNA molecule as in vivo. By using this system as complementation assay, we have purified three DNA replication proteins to homogeneity and identified their functions. B) The Guest Worker (P. Carl) has isolated a mutant which is deficient in RNaseH activity. It has been speculated that RNaseH removes RNA primer from "Okazaki Fragment". We have studied the RNaseH mutant genetically and biochemically. Also, we have cloned and sequenced the RNaseH gene form wild-type and RNase H- E. coli to generate a much tigher mutant of RNaseH by in vitro mutagenesis. C) An in vitro replication system for B. subtilis Phi29 phage has been developed. This system mimics in vivo DNA replication and a protein primes DNA replication.